1. The Field of the Invention
The present invention relates to a safety device used particularly in motor vehicles which, upon the onset of a collision, deploys an inflatable restraint cushion, known as an air bag cushion, to protect the occupants of the vehicle from the impact of the collision. More particularly, this invention relates to an emergency venting system designed to reduce the "punch out" force exerted as the air bag cushion initially breaks out of the cover of the air bag system as it enters the vehicle occupant compartment of a vehicle, thereby reducing the initial impact of the air bag upon an "out-of-position" occupant.
2. The Relevant Technology
An inflatable vehicle occupant restraint, such as an air bag safety system with an inflatable air bag cushion, is inflated to protect an occupant of a vehicle upon the occurrence of a collision. When the vehicle, usually an automobile, is involved in a collision, a crash signal actuates an inflator assembly of the air bag safety system to cause the air bag cushion to deploy. Typically, an actuator triggers the inflator assembly to emit an inflation fluid or gas which flows into an air bag cushion. The inflation fluid rapidly inflates the air bag cushion from an uninflated condition to an inflated condition where the air bag cushion breaks through the outer cover and expands into the vehicle occupant compartment. When the air bag cushion is in the inflated condition, it restrains an occupant of the vehicle from forcefully striking components in the event of a sudden deceleration such as that which typically occurs in a vehicle collision.
The air bag safety system is usually mounted proximate to the seats in the vehicle in which the occupants sit. It is well known to mount the air bag safety system in the steering wheel and/or the instrument panel. Other mounting sites have been used for the air bag safety system. For example, the air bag safety system may be mounted in the door panels or on the side of the seats to protect the vehicle occupant from side impacts.
Under normal circumstances, substantially all of the inflation fluid from the inflator assembly is directed into the air bag cushion to inflate the air bag cushion. One problem associated with rapidly inflating the air bag cushion is that when the air bag cushion is initially breaking out or "punching out" of the cover of the air bag assembly, the initial forces are very high and may potentially injure someone who is too close or "out-of-position" relative to the air bag safety system at the moment of deployment. It is intended that the term "out-of-position" be broadly construed. A vehicle occupant may be "out-of-position" for a variety of reasons. Generally, "out-of-position" means that the vehicle occupant is closer than the predetermined parameters intended.
Because of the potential for injury to an "out-of-position" occupant as well as the high force with which the air bag cushion is initially deployed, there are some circumstances that it may be desirable to control or limit the amount of force with which the air bag cushion "breaks out" or "punches out" of the air bag safety system module. Various techniques have been used to attempt to control the rate of inflation of the air bag cushion. One way of reducing the initial forces exerted as the air bag cushion "punches out" of the storage position is to incorporate remote sensors to detect when a vehicle occupant is too close to the air bag safety system. When the sensors detect that a vehicle occupant is "out-of-position" at the time of deployment of the air bag cushion, the sensor sends a signal to the inflator assembly to reduce and control the rate at which an inflator assembly provides the inflation fluid to the air bag cushion. One problem with this approach is that it significantly increases the complexity of the air bag safety system and, consequently, adds to the expense of the system itself. Further, the complexity of this system makes it more difficult to manufacture, assemble, and maintain the air bag safety system.
Another method of attempting to address the potential injury to an "out-of-position" passenger in a vehicle by initial deployment of an air bag cushion, incorporates a tether inside the air bag cushion. The tether is attached to a valve assembly that has been sewn into the side of the air bag cushion. One type of valve assembly is sewn into the side of an air bag cushion. The valve assembly includes an inner panel which is pleated and folded into a stack over itself when the air bag cushion is uninflated. The inner panel is kept in place by stitching that attaches it to the air bag cushion. One end of the tether is attached to the pleats of the inner panel while the other is attached to the housing or inflator assembly. When the air bag system is actuated, inflation fluid is delivered to the air bag cushion and the air bag cushion begins to inflate. In the event that the air bag cushion encounters an "out-of-position" occupant, the tether is not fully extended and the vents remain open to allow a portion of the inflation fluid to escape the air bag cushion.
If the occupants of the vehicle are in the correct position when the air bag safety system is triggered, as the air bag cushion fully inflates the tether pulls on the inner panel of the valve assembly and severs the stitching holding the inner panel in place. The tether pulling on the inner panel of the valve assembly causes the inner panel to unfold and partially cover the vents. When the air bag is fully deployed the tether continues to pull on the inner panel until the inner panel is completely unfolded and closes off the vent openings. Covering the vents forces the inflation fluid to fill the air bag cushion. In addition to controlling the unfolding of the inner panel, the tether somewhat reduces the expansion velocity of the air bag cushion.
Another method of reducing the force of the air bag cushion as it breaks through the storage cover is to provide the air bag cushion with different types of materials or coatings to allow the inflation fluid to escape should an "out-of-position" occupant be encountered upon deployment of the air bag cushion. Various arrangements have been tried with the fabric of the air bag cushion including using coated, partially-coated, and/or uncoated fabrics with various levels of porosity which permit some of the inflation gas to be exhausted. Another method of addressing the potential for an "out of-position" occupant is to provide one or more vent openings in the wall of the air bag cushion itself to vent the inflation fluid from the interior of the air bag cushion.
The problem with the approaches that add vents, coatings, or valve assemblies to the air bag cushion is that it adds weight to the air bag cushion itself. The added features may also increase the size or thickness of the air bag cushion. This is problematic because manufacturers are consistently trying to reduce the size and/or weight of the air bag safety system. In addition, the additions or changes to the air bag cushion typically require additional parts and steps in the manufacturing process. This results in an increase in the difficulty of manufacturing the air bag cushion. Further, the added weight of the air bag cushion is detrimental to the length of time that it takes for the air bag to be deployed in normal conditions. This may reduce the effectiveness of the air bag safety system.